(1) Field of the Invention
The present invention relates to a shutter structure of aperture, and more particularly to a safety doors blocking on the open ends of the sockets of aperture to prevent any foreign objects from intruding into any socket unexpectedly in normal idle time.
(2) Description of Prior Art
Referring to prior patents of U.S. Pat. No. 3,980,372 and UK patent 2,209,888, among which the U.S. Pat. No. 3,980,372, the shutter door blocking from inside of the open ends of the sockets can not stop a single metal stick or other similar objects breaks in the socket 3 or 4 through the door by pressing down the tilt 9' or 10' at the open 15 or 16; under similar circumstances, the UK patent 2,209,888 is not able to solve the problem--`single inserter opening the shutter door`.